Effect of CaO and SiO2 addition on magnetic properties of anisotropic Ba-Zn system W-type hexagonal ferrite magnets

An experiment was carried out to investigate the effect of CaO and SiO₂ addition on the magnetic and physical properties of anisotropic Ba-Zn W-type hexagonal ferrite magnets. It was found that magnetic properties of BaO.2ZnO.8Fe₂O₃ compounds added with CaO and SiO₂ were improved. The optimum conditions of typical specimens are as follows: chemical analysis composition-Ba_0.857 Zn_1.643 Ca_0.150 Si_0.266 Fe²⁺_0.030 Fe³⁺_15.857 O₂₇; semisintering condition-1275°C × 1.0 h in air; sintering condition- 1250°C × in air, magnetic and physical properties are J_m = 0.436 T, J_r = 0.393 T. H_cj = 64.4 kA/m, H_cB = 64.1 kA/m, (BH)_max = 16.1 kJ/m³, T_c = 357°C, H_A = 971 kA/m, K_A = 2.03 × 10⁵ J/m³ and n_B = 33.2 μ_B.     

Radiofrequency antenna concepts for human cardiac MR at 14.0 T

Objective

To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx).

Materials and methods

RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B₁⁺) uniformity and efficiency in the heart of the human voxel model. B₁⁺ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR_10g) were examined at 7.0 T and 14.0 T.

Results

At 14.0 T static pTx revealed a minimum B₁⁺_ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR_10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B₁⁺_ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B₁⁺_ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR_10g < 5.25 W/kg.

Discussion

MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.

     

Magnetic properties of Pr‐Fe‐Co‐V‐W‐Si‐B system exchange spring magnets

The melt‐spun ribbons of Pr‐Fe‐Co‐V‐W‐Si‐B system alloys were prepared by single roller rapid‐quenching method. The effects of composition, surface velocity, and heat treatment on the magnetic properties were investigated. The P₉sFe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy ribbons prepared at a surface velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat‐treatment condition was found to be at 575°C for 3 min, for which the magnetic properties were (BH)_max = 136.1 kJ/m³, J_r = 0.93 T, H_cJ = 652.2 kA/m, and H_cB = 528.3 kA/m. The temperature coefficients of J_r and H_cJ for the ribbons crystallized from melt‐spun ribbons of Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy were α(J_r)_ave = ?0.057%/°C and α(H_cJ) = ?0.450%/°C. The value of (B)_max for the compression molding Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 isotropic bonded magnet prepared by using the ribbons annealed at 575°C for 3 min is 80.0 kJ/m³, and the density is 6.24 Mg/m³. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 10–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20211 Copyright © 2006 Wiley Periodicals, Inc.     

Fluorine-19 MRI at 21.1 T: enhanced spin–lattice relaxation of perfluoro-15-crown-5-ether and sensitivity as demonstrated in ex vivo murine neuroinflammation

Objective

Fluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of ¹⁹F MR that can be practically achieved when moving from 9.4 to 21.1 T.

Materials and methods

We studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B₀), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B₀ with 2D-RARE and 2D-FLASH using ¹⁹F volume radiofrequency resonators together. T₁ and T₂ of PFCE were measured at both B₀ strengths.

Results

Compared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of ¹⁹F T₁ and T₂ relaxation on B₀ was demonstrated. High spatially resolved ¹⁹F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T.

Discussion

Enhanced SNR and T₁ shortening indicate the potential benefit of in vivo ¹⁹F MR at higher B₀ to study inflammatory processes with greater detail.

     

Properties of anisotropic Ba‐Zn‐Cu system W‐type hexagonal ferrite magnets

Experiments were carried out to investigate the magnetic and physical properties of Ba‐Zn‐Cu W‐type hexagonal ferrites sintered without atmosphere control. Compositions were chosen according to the formula BaZn_2–xCu_xFe₁₆O₂₇, where x was varied 0 ˜ 0.5 and 1.0. The effect of BaO addition after semisintering treatment on magnetic properties of Ba‐Zn‐Cu compounds was examined. It was found that BaO addition for Ba‐Zn‐Cu compounds was very useful in stabilizing the W‐type hexagon. The optimum condition of making magnets and some properties of typical specimens are as follows: composition—BaZn_1.7Cu_0.3Fe₁₆O₂₇ with 4 wt% Ba added; semisintering conditions—1275 °C for 1.0 h in air; sintering conditions—1175°C for 0.5 h in air; magnetic properties and lattice constant are J_m = 0.405 T, J_r = 0.370 T, H_cJ = 88.15 kA/m, (BH)_max = 19.12 kJ/m³, T_c = 356 °C, H_A = 994.7 kA/m, K_A = 2.01 × 10⁵ J/m³, c = 32.928 × 10^–10 m, a = 5.927 × 10^–10 m, c/a = 5.556. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 36–42, 2001     

Die Verformung extrem kurzer Impulsflanken an Störstellen in Leitungen mit übergroßem Querschnitt

Übersicht Die Verlangsamung von Impulsflanken durch Wirbelströme. Einsatz von Leitungen mit übergroßem Querschnitt zur Übertragung sehr kurzer Impulse. Verformung von Impulsflanken durch sprunghafte Querschnittsänderungen und Ecken. Kreisrunder Stift in der Parallelplattenleitung. Experimentelle Bestätigung der Ergebnisse für den Querschnittssprung.

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Contents Degradation of fast rise times due to skin effect. Transmission of high speed pulses by oversized transmission lines. Waveform distortion due to step discontinuities and beuds. Circular cylinder within a parallel-plate waveguide. Experimental check on the analysis of the step discontinuity.

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Verzeichnis der verwendeten Symbole A ⁱ,B ⁱ Amplituden der anregenden Wellen - A _m ,B _m Koeffizienten angeregter Wellen - Lichtgeschwindigkeit im Vakuum - D _ln Faktoren, die die Kopplung zwischen Feldern in der Ecke und in der Plattenleitung beschreiben - f _nA ,f _nB Grenzfrequenzen derE _on -Wellen in den LeitungenA, B - H()=U ₂/U ₀ Systemfunktion - H _n ⁽²⁾ =J _n –j N _n Hankelsche Funktion 2. Art der Ordnungn - imaginäre Einheit - J _n Besselsche Funktionn-ter Ordnung - k=/c ₀ Wellenzahl - k _rmA ,k _rmB Eigenwerte derE _on -Welle - k _zmA ,k _zmB Wellenzahlen derE _on -Welle - N _n Neumannsche Funktionn-ter Ordnung - P _mn Koppelintegrale - T _A0,T _A2 Anstiegszeiten von anregendem, Signal und Ausgangssignal (gemessen von 10%–90% des Endwertes) - T _S Schwingungsdauer der gedämpften Schwingung - u ₀(t),u ₂(t) zeitabhängige Spannung der anregenden Welle, zeitabhängige Ausgangsspannung - ₀(), ₂() Fourier-Transformierte vonu ₀(t),u ₂(t) - U ₀,U ₂ Sinusspannungen - Kehrwert vonZ ₀ - Y _mA ,Y _mB Kehrwerte der Feldwellenwiderstände derE _on -Wellen - Feldwellenwiderstand des Vakuums - Z _A ,Z _B Wellenwiderstände der Koaxialleitung - _{l m} Kronecker-, _{l m} = 1 fürl = m, _{l m} = o fürl m - _{m A} , _{m B} Eigenfunktionen - =2··f Kreisfrequenz Die Arbeit ist entstanden im Institut für Elektrische Nachrichtentechnik der Universität (TH) Stuttgart, 7 Stuttgart 1, Breitscheidstr. 2.     

Magnetic properties of melt-spun Nd-Fe-Co-B-Cu-Nb system alloys and their bonded magnets

Melt-spun ribbons of Nd-Fe-Co-B-Cu-Nb system alloys were prepared by the single roller rapid-quenching method. The effects of composition, wheel velocity and heat-treatment on the magnetic properties were investigated. The magnetic properties of bonded magnets prepared by compression molding of optimally annealed ribbons were also measured. A maximum energy product of 152.1 kJ/m³ was obtained for the Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 alloy ribbon prepared at a wheel velocity of 17.1 m/s. From the TEM observation on the above Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 ribbon, the particle size of these ribbons was determined to be between 10 and 40 nm. It is conjectured that the high remanence is observed by the magnetic interaction of these fine particles, and it was found that these fine particles were achieved by Nd-Fe-Co-B compound in addition with Nb and Cu at the same time. The amorphous Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 15 min. Its corresponding value of (BH)_max is 144.5 kJ/m³. A maximum energy product of 88.1 kJ/m³ was achieved with Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 bonded magnets made from the optimally prepared ribbons.     

Stationary thermal field in a long duct of an electrical heating system

Contents The subject of this work is the analysis of a stationary thermal field in a long duct of an electrical floor heating system. Parallel sectors of the heating cable are modelled by heat sources of the emitted power linear density. The resultant thermal field is described by a partial differential equation of the elliptic type with boundary conditions of the second and third kind. The problem is solved by the method of eigenfunctions. The results are reduced to a dimensionless form and numerically processed. The field distributions obtained are presented in graphical form, with the number of sectors of the heating cable in the duct being changed.

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Das stationäre Temperaturfeld im langen Kanal einer elektrischen Fußbodenheizung

Übersicht Der Artikel analysiert das stationäre Temperaturfeld im langen Kanal einer elektrischen Heizung. Parallele Kabelstrecken wurden durch Wärmequellen ersertzt. Das Temperaturfeld wird mit Hilfe der partiellen Differentialgleichung des elliptischen Typs dargestellt. Dieses Problem hat man durch die Eigenfunktion gelöst. Die Ergebnisse wurden in eine dimensionslose Form umgewandelt und numerisch bearbeitet. Die Feldverteilungen wurden graphisch dargestellt, wobei die Anzahl der Kabelabschnitte verändert wird.

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List of symbols A dimensionless constant, determined by (6b) - 2a, 2b dimensions of the cross-section of the duct (Fig. 1.) - B _mm coefficient of the series (5), determined by (8) - c _k relation of linear density of the power of heaters; thek-th to the first (q _k /q ₁) - K number of heaters - k index of thek-th heater (k=1,2,...,K) - L(x/2b, y/2b) total dimensionless thermal field in the duct - L _k (x/2b, y/2b) dimensionless component of thermal field caused by thek-th heater (with the others turned off) - q _k linear density of the power of thek-th heater [W/m] (k=1,2,...,K) - S cross-section of the duct - T=T(x, y) total temperature field in the duct - T _k (x, y) component of the temperature field in the duct caused by thek-th heater (with the others turned off) - T ₀ temperature of air far from the top surface of the duct - v _k (x, y)=T _k (x, y)–T ₀ k-th component of an increase in the thermal field in the duct over the valueT ₀, caused by thek-th heater (with the others turned off) - (x, y) Cartesian coordinates of a point in the duct - (x _k ,y _k ) coordinates of the position of thek-th sector of the heating cable, averaging coefficient of heat transfer to air (sum of the radiation and convection coefficients) [W/(m ² K)] - averaging coeffiecient of heat transfer to air (sum of the radiation and convection coefficeints) [W/(m ² K)], - _n successive positive roots of (6a), (6b) - (x–x _k ), (y–y _k) Dirac's deltas shifted tox _k andy _k respectively - _m0 Kronecker's symbol - averaging heat conductivity of micro-reinforced concrete [W/(mk)]     

Evaluation of photovoltaic modules considering spectral solar radiation

For the optimum design of photovoltaic power systems, it is very important to estimate their annual maximum amount of output. In general, the annual maximum amount of output has been calculated by using photovoltaic module efficiency under irradiance of 1 kW/m² at AM 1.5 with solar cell temperature of 25°C. Since the spectral distribution of solar radiation changes with weather, season and time, the efficiency of solar cells is not always constant. This paper describes a method evaluating the maximum amount of output in photovoltaic modules, ‘the spectral method,’ by using the measured annual spectral solar radiation and the spectral response of various photovoltaic modules. The calculated values using the spectral method agreed well with the measured values for amorphous silicon photovoltaic modules from March 1991 to February 1992. The spectral method proved most effective for optimum design of amorphous silicon photovoltaic power systems.     

Quadratic programming approach to reactive power optimization on the primary feeders

Contents In this paper we suggest the use of the quadratic programming technique to determine the optimum size and location of shunt capacitors on radial distribution feeders so as to maximize overall savings, including the cost of capacitors. The saving function which is of quadratic form is maximized for a set of linear inequality constraints by using quadratic programming. — For quadratic programming, efficient alogrithms have been developed which can easily be implemented on digital computers. — The approach is illustrated by an application to a typical distribution feeder of 23 kV.

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Blindleistungsoptimierung an primären Einspeisungen mit Hilfe quadratischer Programmierung

Übersicht Diese Arbeit stellt die Anwendung der quadratischen Programmierung zur Ermittlung optimaler Werte und Orte von Parallelkapazitäten an radialen Verteilungen mit dem Ziel der Kosteneinsparung vor. Die Methode ist an einer 23-kV-Verteilung entwickelt und überprüft worden.

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Nomenclature A M×N array of constraint coefficients - B M vector of constrain limits - C N×M array of quadratic coefficients, from objective function - E Energy loss caused by reactive current in the feeder - E Reduction in energy loss - I _ck Capacitor current injected at nodek - Î _k Maximum reactive load current at nodek - K _c Annual cost per unit of installed capacitor ($/A) - K _E Per unit energy production cost ($/kWh) - K _P Annual cost per unit of power loss ($/kW) - m _k Reactive load factor for loadk - M Number of constraints - N Number of structural variables - P N vector of linear term coefficients from objective function - P Peak power loss caused by reactive current in the feeder - P Reduction in peak power loss - R _k Line resistance for sectionk - S Net saving resulting from peak power and energy loss reduction - T Total period of the reactive load curve - X _k Line reactance for sectionk     

Magnetic properties of melt-spun Nd-Pr-Fe-Co-B-V system alloys and their bonded magnets

Melt-spun ribbons of Nd-Pr-Fe-Co-B-V system alloys were prepared by the single-roller rapidquenching method. The effects of composition, wheel velocity and heat treatment on the magnetic properties were investigated. The magnetic properties of their isotropic compression bonded magnets prepared from optimally annealed ribbons also were measured. Remanence (Br) was found to increase with decreasing rare-earth content, and a maximum value of more than 1.0 T was obtained. A maximum energy product of 164.0 kJ/m³ was obtained for (Nd_0.5 Pr_0.5)₉Fe₄Co₈B_7.5 V_1.5 alloy ribbon prepared at a wheel velocity of 17.1 m/s. From TEM observation, the particle size of these ribbons was determined to be between 20 to 30 nm. It is conjectured that the high remanence is obtained by the interaction of these fine particles. The amorphous (Nd_0.5Pr_0.5)₉Fe₇₄Co₈ B_7.5V_1.5 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 20 min. Its corresponding value of (BH)_max was 146.2 kJ/m³. A maximum energy product of 86.4 kJ/m³ was achieved with (Nd_0.5Pr_0.5)₉Fe₇₄Co₈ B_7.5V_1.5 bonded magnets made from the optimally prepared ribbons.     

Die optimale Projektierung eines magnetischen Kreises mit Dauermagnet für Lautsprecher

Übersicht Der magnetische Kreis des Lautsprechers ist eine wichtige Anwendung der harten Ferrite. Das Kennen des magnetischen Streuflusses und folglich die optimale Projektierung dieses magnetischen Kreises ist von großer Bedeutung, wenn man das mögliche Magnetstoffersparnis berücksichtigt. In der vorliegenden Arbeit wurde eine Methode zur Optimierung des magnetischen Kreises mit Dauermagnet für Lautsprecher angegeben, wobei die Berechnungen durch die Integration der Feldgleichungen durchgeführt werden.

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Contents The magnetic circuit of the loudspeakers is an important application of hard ferrites. The knowledge of the magnetic leakage flux and consequently the optimum design of this magnetic circuit is of great importance, because of the possible economy of magnetic materials. In this paper a method for optimisation of magnetic circuits with permanent magnet for loudspeakers is presented. The calculations were performed by integration of field equations.

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Übersicht der verwendeten Symbole A Querschnitt des ringförmigen Dauermagneten - A Querschnitt des Luftspaltes - a, b, c, d, g, h, l, Abmessungen des magnetischen Kreises - a ⁰ =a + ⁰ (Bild 2) - B _m =B mittlere Induktion im Inneren des Dauermagneten - B Induktion im Luftspalt - F hypergeometrische Funktion - G Hilfsfunktion für die Berechnung der Streuung im Bereich III - H _m =–H mittlere Feldstärke im Inneren des Dauermagneten - k _n Nutzfaktor - P _m optimaler Betriebspunkt (Bild 1) - P ₀ maximaler Punkt der KennlinieB _m =f(B _m H _{m 0})(Bild 1) - V _I,V _II,V _III magnetische Potentiale der inneren (I), oberen (II) und äußeren (III) Zone - V ₀ magnetisches Potential der Polplatte - v Volumen des Dauermagneten - v Volumen des Luftspaltes - T - u ₂ Hilfsveränderliche (Beziehung (24) - z, r zylindrische Koordinaten - ⁰ äquivalenter Luftspalt, der eine Potentialstufe bestimmt, die durch die äußere Fläche des Bolzens denselben Fluß wie das reelle Potential erzeugt - ^* äquivalenter Luftspalt, der eine Potentialstufe bestimmt, die durch das Ende des Bolzens denselben Fluß wie das reelle Potential erzeugt - ⁰=4·10^–7 (H/m) Vakuumpermeabilität - Streufaktor - ₀ Gesamtfluß, der in den Magneten durch seine Basis eindringt - _I, _II, _III Teilstreuflüsse (Bild 2) - _n Hauptfluß im Luftspalt - _s gesamter Streufluß - _s magnetischer Bezugsfluß - ^* = 4a V _{0 0} Hilfsfunktionen für die Berechnung der Streuung im Bereich I     

Rectifier circuits for optimal frequency conversion

It is proved that a circuit consisting of non-linear passive resistances and of any linear invariant passive elements cannot convert power from frequencies ω₁ and ω₂ into power at frequency mω₁ + nω₂ with an efficiency better than 1/(|m| + |n|)². Circuits attaining that efficiency are constructed for all m, n, so that the condition is both necessary and sufficient. For m = μt, n = vt, |μ| + |v| = 2^s (all literals are integers), the optimal circuit consists of a finite number of rectifiers and tuned circuits. For values of m, n that are not of the above form an infinite number of tuned circuits is necessary, but an efficiency better than 93 per cent of the optimum is attainable by simple finite circuits in all cases.     

Non‐unique solutions in drift diffusion modelling of phototransistors

We report non‐unique solutions for the potential in a Drift Diffusion (DD) model of a two terminal phototransistor. These solutions are present under bias without illumination, and persist until high illumination levels. It is well known that the DD equations can yield non‐unique solutions for pn structures which contain three or more junctions and two terminals with applied biases greater than k_BT log 2 where k_BT is the thermal energy at a temperature T, but DD models of phototransistors under illumination have been less well studied. The implicit belief is that one needs to artificially impose a potential in the base of the phototransistor in order to obtain a unique solution. We show here that this is only necessary because of a weakness in the numerical methods used to solve the equations, and describe two methods which circumvent this for which we show that this problem does not occur. These methods are used to investigate the operation of GaAs and In_0·53Ga_0·47As homojunction phototransistors, including the influence of the position of the illumination region and base doping. Copyright © 2000 John Wiley & Sons, Ltd.     

Characteristics of photovoltaic/fuel cell power hybrid system. (Effect on electrical load form factors)

The photovoltaic power system has a great future as a clean-energy alternative to fossil fuel which has many environmental problems such as gas exhaustion or air pollution. Sunlight, a source of energy for the system, is influenced greatly by weather conditions, seasons and times of day. Therefore it cannot supply constant electric power. The photovoltaic/fuel cell power hybrid system is assumed. It combines PV array, hydrogen generator, storage tank and fuel cells by using hydrogen. This system can supply constant electric power to the electric load in a solitary island separated from a commercial electric network. The possibility of this system is examined by computer simulation. Input data include the global irradiance on inclined plane and temperature of HASP data of Tokyo, ten kinds of electrical load forms with 400 MWh electric power a year, and conversion efficiencies of each subsystem. As a result of simulation, it was revealed that the area of PV array with 8170 m² and the volume of hydrogen tank from 22 × 10³ to 30 × 10³ kl are necessary.     

Nd–Fe–B thick films prepared at the high deposition rate of 90 µm/h

After a postannealing process, the magnetic properties of pulsed laser deposition (PLD)‐made Nd–Fe–B film magnets prepared at the deposition rate of 20–90 µm/h showed constant values, and the average values of H_c, B_r and (BH)_max were 1050 kA/m, 0.6 T, and 60 kJ/m³, respectively. The obtained results were comparable to those previously reported. In conclusion, it was found that a maximum deposition rate of 90 µm/h could be achieved without deterioration of magnetic and mechanical properties. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Synthesis of magnetic fields by optimization of the shape of areas and source distributions

Contents The paper deals with a practical method for the synthesis of two-dimensional magnetic fields. The proposed algorithm makes it possible to determine the optimal structure of areas and optimal source distribution which generate the required magnetic fields. The main idea of this algorithm is based on the application of a modified gradient method for solving the overdetermined, nonlinear system of algebraic equations obtained by the finite element method. Numerical calculations performed in 5 examples demonstrate possible applications of the proposed method.

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Synthese von Magnetfeldern durch Optimierung der Gebietsformen und Quellenverteilungen

Übersicht Die Arbeit behandelt eine praktische Methode zur Synthese von zweidimensionalen Magnetfeldern. Das vorgeschlagene Verfahren ermöglicht die Berechnung der optimalen Form von Gebieten und optimalen Quellenverteilungen zur Erzeugung vorgegebener Magnetfelder. Die Grundidee des Berechnungsverfahrens basiert auf der Anwendung einer modifizierten Gradientenmethode zur Lösung von nichtlinearen, überbestimmten Gleichungssystemen, die mit der Methode der finiten Elemente entwickelt wurden. Numerische Berechnungen von 5 Beispielen illustrieren die Anwendungsbreite der vorgeschlagenen Methode.

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List of main symbols A,A vector potential - J, J current density - M,M _x ,M _y magnetic polarization - _x , _y reluctivity - _r permeability - e _x ,e _y ,e _z unit vectors - B,B _x ,B _y flux density - B _o ,B _ox ,B _oy flux density in the synthesis region - G region under investigation - G ₀ synthesis region - F functional - Q quality criterion - r ^k direction vector - r ₀ minimal least squares solution - e error vector - z solution vector - _min step-length factor - D Jacobi matrix - R Moore-Penrose pseudoinverse - ₁, ₂, ₃ error criterion - N number of points - m number of equations - n number of unknowns     

Analysis of work of liquid metal induction pump

Contents In the paper the finite element method is presented so as to determine electromagnetic field distribution in a cylindrical liquid metal induction pump. The effect of exciting current frequency, the channel width and the channel material conductivity on dynamic parameters of the pump has been analysed. — The obtained calculation results have been shown in the graphs.

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Analyse der Pumpe für ein flüssiges Metall

Übersicht Im Beitrag wurde die Methode der finiten Elemente zur Bestimmung der Verteilung des elektromagnetischen Feldes in einer zylindrischen Pumpe für ein flüssiges Metall verwendet. Man hat den Einfluß des Erregerstroms, der Kanalbreite und der Leitfähigkeit des zum Aufbau des Kanals benutzten Stoffes — auf die dynamischen Parameter dieser Pumpe untersucht. Die erhaltenen Ergebnisse hat man in Form von Diagrammen dargestellt.

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List of symbols A vector potential - A vector potential (complex r.m.s. value) - A z-component of vector potential (complex r.m.s. value) - A _i ,A _j ,A _k vector potential values in nodal pointsi, j, k (complex r.m.s. values) - B magnetic induction - B magnetic induction (complex r.m.s. value) - B _x ,B _y components of magnetic induction (complex r.m.s. values) - F _t electrodynamic force - F mean force - F _a alternating force - F _x ,F _y components of the mean force - conductivity of the liquid metal - J current density (complex r.m.s. value) - J _a current density - J _w exciting current linear density (complex r.m.s. value) - l length of the channel - magnetic permeability of the liquid metal - M torque acting upon the liquid metal - current pulsation - p pressure of transported metal - Q pump efficiency - v _x ,v _y components of the liquid metal's velocity in the 0X and 0Y direction - z ^* conjugate complex number ofz     

The Electrical Conductance of SrFeO2.5+x Thin Films

Thin films of the non-stoichiometric perovskite SrFeO_2.5+x have been grown by the pulsed excimer laser deposition technique onto sapphire substrates. The electrical conductance properties of the thin films have been determined in a series of experiments done both isothermally and with programmed temperature changes from ambient to 490°C and under O₂/N₂ atmospheres with oxygen concentrations in the range from 100 ppm to 100%. Over these ranges of temperature and oxygen partial pressure a wide range of oxygen stoichiometry in SrFeO_2.5+x occurs (approximately 0 < x < 0.5), which includes all four known phases in the SrFeO_{2.5 + x} + O₂ system. The experimentally measured values for the activation energy of conduction, _A, for SrFeO_2.5+x films at temperatures 100 < T < 200°C are in the range 0.30 < _A < 0.47 eV under oxygen at partial pressures 0.001 O ₂)< 0.05 atm and 0.18 < _A < 0.28 eV for 0.2 O ₂)< 1 atm. These values for _A are typical for compositions of SrFeO_2.5+x with stoichiometries in the range 0.25 < x < 0.45. For T < 300°C and for P(_{O 2})< 0.001 atm the films were essentially insulators. For T > 250^°C and P(_{O 2})> 0.001 atm, the oxygen stoichiometries of the films change during the programmed temperature ramps. For these conditions, the values _A/ T exhibit minima/maxima in the temperature range 250 < T < 320^°C which are interpreted as being due to the onset of the order-disorder phase transition from the cubic to the tetragonal and orthorhombic ordered phases of SrFeO_2.5+x with oxygen stoichiometry in the range 0.08 < x < 0.38. The SrFeO_2.5+x thin films have application as oxygen sensing materials, and a relationship between conductance and oxygen sensitivity, S _ox , has been derived. The values of S _ox for SrFeO_2.5+x thin films increases by more than an order of magnitude for compositions close to the lower stoichiometric limit where the principal phase conversion is between the cubic perovskite and the brownmillerite forms.     

Magnetic properties of iron-based materials (nitrogen interstitially modified 1:12 compounds and Fe3B-Nd) for low rare-earth bonded magnets

Hard magnetic properties of nitrogen interstitially modified NdM_xFe_12-xN_y compounds and Fe₃B-based ultra-fine crystalline Nd? Fe? Co? T? B alloys of low Nd content of 3 to 5 at. % are studied. The nitrogen-modified compounds have been prepared via the rapid solidification route and the mechanical alloying route both followed by gas nitrogenation using N₂. The Fe₃B-based materials have been prepared by means of rapid solidification and crystallization treatment. The latter materials appear promising as the base material for high-remanence, easy-to-magnetize bonded magnets with small temperature coefficients of remanence. Typical magnetic properties of compaction isotropic bonded magnets produced from this material are B_r = 0.80 T, H_cJ = 350 kA/m, and (BH)_max = 60.5 kJ/m³.